This invention relates to a brake pressure control unit for regulating a hydraulic brake pressure supplied from a master cylinder to at least one the wheel brake cylinders depending upon a load on the vehicle suspension.
In order to reduce the possibility of skidding in the rear wheels, it is necessary to have the hydraulic brake pressure at the rear brakes increase at a reduced rate with respect to front wheel brake pressure in accordance with the load of the vehicle. In view of safely driving, the hydraulic brake pressure from the master cylinder is distributed to the wheel brake cylinders in such a manner that the front wheel locking state occurs precedently rather than the rear wheel locking state. Refer to FIG. 4 wherein the mutual relationship of the hydraulic brake pressure within the front wheel cylinders and the rear wheel cylinders is shown, a brake pressure control unit is designed in practice to locate lines (A, A ') for real braking effort below lines (B, B') for ideal braking effort, thereby establishing a tendency of the front wheel preceding locking state. However, since the lines (A, A') for real braking effort are linear and the lines (B, B') for ideal braking effort are a curve of secondary degree, respectively, the brake pressure control unit is provided with a load sensing proportional valve (so called P-valve) to form split or broken points (C, C') so as to bring the lines (A, A') close to the lines (B, B').
To obtain the afore-mentioned real braking effort lines, a conventional brake control unit is generally constructed in such a manner that the P-valve secured a vehicle's body (a chassis frame side) is arranged to be connected with the master cylinder and the rear wheel cylinders and a load sensing lever swingable about a pivot point abuts on a plunger of the P-valve, its free end being connected operatively to a bracket on the axis side by way of a coiled spring. In this construction, the dimensional relation between the chassis frame and the bracket on the axis side is varied depending upon the extent of the current load of the vehicle and this variation is transmitted to the load sensing lever so as to push the plunger of the P-valve to a corresponding extent to such the effect on the lever, so that the split points can be optimally selected on the real braking effort lines due to the variation of the change-over pressure point of the P-valve.
This type of a brake pressure control unit is known from the disclosure of U.S. Pat. No. 4,639,048 in which a lever abutting on a plunger of the P-valve is connected through a threaded spindle and a spring device with a bracket on the axis side. In this conventional unit, the spring device is equipped with a spacing element in the shape of a distance gauge to eliminate play of the lever with respect to the P-valve and select a distance between two positions of a spring pivot point, and the brake pressure control unit with the P-valve and the spacing element is installed in the unloaded vehicle. After mounting the brake pressure control unit and adjusting the freedom of play of the lever, the spacing element is removed from the spring device.
It is a disadvantage in the conventional brake control unit as afore-mentioned that the space element is essential to keep the biasing force of the spring constant and has to be removed from the spring device after mounting of such unit on the unloaded vehicle and adjustment of the freedom of play of the lever. This will increase labor costs and result in an increase of the costs of the whole brake pressure control unit.